January 20, 2012

Arxiv - Researchers describe a new system for a society of highly advanced civilizations around a super massive black hole (SMBH), as an advanced Type III “Dyson Sphere,” pointing out an efficient usage of energy for the advanced civilizations. SMBH also works as a sink for waste materials. Here we assume that Type III civilisations of Kardashev classification [1] form a galactic club [2] in a galaxy, and the energy from the SMBH will be delivered to the club members, forming an energy control system similar to power grids in our present society. The energy is probably transmitted by a sharp beam with coherent electro-magnetic waves, which provide a new concept for the search for extraterrestrial intelligence (SETI) via detection of such energy transmission signals. This expands the search window for other intelligences within the Universe.

The condition around a SMBH at the centre of galaxy would be more efficient both in extracting energy and exhausting the waste energy for advanced civilizations, than those of a Dyson Sphere. Some active galactic nuclei (AGN) are extremely luminous, hundreds of times the integrated stellar luminosity of a whole galaxy. For example, bolometric luminosity of QSOs and Seyfert galaxies is distributed mostly in a range between 10^43-10^47 erg/s

Schematic picture around SMBH. Items are not to scale. In this picture, an example of power plants with transmitters is shown partly. BLR stands for the Broad Line Region. The SMBH and accretion disk will not be fully covered by the collectors of power plants, so as not to prevent jets emanating from somewhere in this area, and accretion flow coming out of the central region. A twin jet is thought to emanate perpendicular to the plane of accretion disk, seen about 10% of AGN. The energy from the power plants is transferred by electro-magnetic waves to habitats of advanced civilizations. In this picture, the beams are directed to a galactic plane on which a galactic club is formed. However, the planes of the accretion disk and the host galaxy may not necessarily be in the same plane (e.g., Inoue). One Rs for the SMBH mass of 10^8 M is ~10^-5 pc (3 × 10^8 km).

The radius of SMBH in the center of a galaxy is about 2 astronomical units (twice the distance of the earth orbit around the Sun).The diameter of an accretion disk is likely the size of our solar system, comparable to Dyson Sphere of stellar scale Type II civilizations, while the energy scale is more than 10^8 times larger than that, i.e., the integrated stellar energy of the whole galaxy.

Radiation from the accretion disk will be collected by a mirror system as a Type III “Dyson Sphere.” Waste material and energy could be thrown off toward the central SMBH, and the SMBH would be the final reservoir for all of the waste materials for any civilizations. Thus, the most advanced civilizations would develop their activities using a SMBH efficiently, putting the power plants around the SMBH at the centre of their home galaxy. We discuss a possible model of such system, and the possibility to detect indicators of the existence of the system, or such civilisations.

Power Plant around SMBH

The structures of the power plant basically revolve around the central SMBH in Keplerian motion to form “Dyson Shells.” In an advanced case of Type II, the central star is almost fully covered to form “Dyson Sphere”. Here we discuss the case of structures partly covered, or the Dyson Shell type, and call it a Dyson Sphere. Unlike a stellar environment, or Type II Dyson Sphere, there are complex structures like relativistic jets, accretion disk and accreting matters, rapidly rotating stars, etc., and hence it would be very difficult to construct a fully covered structure, like a system studied by Birch over a large gaseous planet (e.g., Jupiter). However, it is not easy to set numbers of power plants with similar distance orbiting around the central SMBH. Hence, it would be a possible solution to set the power plants on a solid framework, something like structures studied by Birch. Some areas should be kept uncovered to yield emanating jets and accreting flows.

First, we estimate the distance where iron melts by radiation, assuming 10^45 erg/s comes from a central point source. Given this luminosity is generated by 10% of the Eddington luminosity, the SMBH mass corresponds to 7 × 10^7 M. The melting point of iron is 1800 K, and at 0.75 pc (2.3 × 10^13 km) from the central source, temperature becomes the melting point. It would be possible to use material with a high reflection coefficient (i.e., large albedo) and high melting point, and as the distance is inversely proportional to temperature square, the area of 0.1 pc (3 × 10^12 km) from SMBH would be available to construct the structures. This area corresponds ~10^4 Rs for M ~ 10^8 M.

The power plants will be set off-plane of the accretion disk or outside of the outer edge of it to avoid its orbit crossing the disk. Then, the distance from the central SMBH might be 1,000 Rs or more, and the tidal force should not be a serious problem for the structure of the power plant. As the tidal force at a distance R from a SMBH (gravity centre) is inversely proportional to R3, and Rs is proportional to M, the tidal force decreases with mass of SMBH. For example, the tidal force at 10 Rs is already 10^-3 times smaller than that at the surface of the Earth, for the case of 10^8 M. As the power plants are supposed to set far out from 10 Rs and the tidal force decreases with R-3 from the central SMBH, we will not care about the tidal disruption of the structure in the power plants anymore.

Each power plant would transmit collected energy as a collimated microwave beam from a 100-mile diameter antenna.

Or, aliens might use molecular interstellar clouds to fashion an efficient transmission system, by means of a maser. A maser (an acronym for Microwave Amplification by Stimulated Emission of Radiation), creates an intense coherent beam of radiation when atoms or molecules in a gas, liquid or solid medium, force an incoming mix of wavelengths to work in phase, or, at the same wavelength. This would amplify radiation from the accretion disk and make a sharp collimated beam.

Nature has already fashioned mega-masers in clouds near galactic black holes, and therefore radiation pumping by artificial means may not be so difficult to set up.

But could we detect evidence of such a mega-engineering project? Probably not say the authors, because the energy would be highly beamed and therefore only be visible if you were along the line-of-sight.

The condition around SMBH is very promising for an advanced intelligence to manage energy issues in terms of both energy generation and disposition. This idea comes from a combination of Type III and Dyson Sphere. The strong radiation from the accretion disk rotating around SMBH is mainly used, and the waste energy is returned toward the SMBH. The available energy is huge compared to Dyson Sphere of stellar scale, and this type of civilization could be called Type III Dyson Sphere. The search for this type of civilization, however, would not likely be revealed from “unintended” communication signal, but detection by coherent radiation from power stations may be more promising.